Diversified light sources, e.g., incandescent light bulbs, fluorescent lamps and light emitting diodes (LEDs), are commonly present in people's daily lives. LEDs, featuring advantages of high efficiency, a long life cycle, resistance to damages, a fast response speed and high reliability superior to that of conventional light sources, are extensively applied in various fields.
Light modulation of LEDs are mainly categorized into linear modulation and pulse width modulation. For example, the European Patent Publication No. EP 1814365 discloses “LED driving device with pulse width modulation”. The above disclosure includes a pulse width modulation (PWM) control unit and an LED driving circuit. The light emitting duration in a PWM period of the PWM control unit is mainly divided into a primary light emitting period and a secondary light emitting period. The primary light emitting period is further divided into multiple small periods that are then distributed throughout the entire PWM period, so as to increase the number of times and the refresh rate of light emitting and to prevent issues of discontinuous images or glittering.
The above conventional solution solves the issues of discontinuous images and glittering. One principle of pulse width modulation is that, continuous linear light is generated through vision persistence of human eyes, and the issue of glittering may remain undiscovered to the human eyes by increasing the refresh rate. However, fundamentally speaking, switching switches at a fast speed causes a large instantaneous current to flow into the LED to potentially shorten the life cycle of the LED. Further, as the ambient temperature changes, semiconductor components in a circuit change the value of an inputted current, and the color temperature of the LED is caused to drift. Therefore, it is a goal of the industrialists of the field to provide a solution that prevents the color temperature of the LED from drifting with a change in the ambient temperature.